test.js

function Car(listedPrice) {
   var price = listedPrice;
   this.speed = 0;
   this.numWheels = 4;

   this.getPrice = function() {
       return price;
   };
}

Car.prototype.accelerate = function() {
   this.speed += 10;
};

function ElectricCar( listedPrice ) {
    // add an 'electricity' property to this class

    var price = listedPrice;
}

ElectricCar.prototype = new Car();

// Add refuel method here:
ElectricCar.prototype.refuel = function(    ) {

};

myElectricCar = new ElectricCar(500);